Method and system for controlling vacuum

ABSTRACT

An engine with a two vacuum sources is disclosed. In one example, a valve position is adjusted in when engine load is low and intake manifold pressure is low to arbitrate vacuum between the two vacuum sources. The approach may increase engine operating efficiency during at least some conditions.

BACKGROUND/SUMMARY

Vacuum may be used to operate or to assist in the operation of variousdevices of a vehicle. For example, vacuum may be used to assist a driverapplying vehicle brakes. Further, vacuum may be used to adjust theposition of a turbocharger waste gate or a turbocharger vane position.Vacuum is often obtained from an engine intake manifold in normallyaspirated engines because the intake manifold pressure is often at apressure lower than atmospheric pressure. However, in boosted engineswhere intake manifold pressures are often at pressures greater thanatmospheric pressure, intake manifold vacuum may replaced or augmentedwith vacuum from a pump. In systems that rely on intake manifold vacuumand/or pump vacuum, pressure controlled check valves may be used tocontrol vacuum of a reservoir that assists actuator operation. Forexample, if engine intake manifold pressure is low, air may be drawnfrom a vacuum reservoir to the engine intake manifold via a pressurecontrolled check valve. However, if engine intake manifold pressure ishigh, the pressure controlled check valve may limit air flow from theintake manifold to the vacuum reservoir. In this way, vacuum thatassists actuator operation of a vehicle system may be controlled.

Pressure controlled check valves have known operating characteristicsand are inexpensive. However, pressure controlled check valves may openor close during engine operating conditions when it may not be desirableto do so. For example, if an engine is operating at a low load conditionand an opening area of the air intake passage throttle is small, vacuumin the engine air intake manifold may cause a pressure controlled valveto open such that air flow to the engine increases beyond a desiredamount. As a result, engine spark may be retarded so that the desiredengine torque is provided. However, increasing the engine spark retardcan decrease engine efficiency and increase engine fuel consumption.

The inventors herein have recognized the above-mentioned disadvantagesand have developed an engine operating method, comprising: operating anengine at a condition where a intake throttle is substantially closed;and closing a valve to limit engine air flow from a vacuum reservoir tothe engine intake manifold when a pressure in the engine intake manifoldis less than a pressure in the vacuum reservoir.

By closing a valve between a vehicle vacuum reservoir and an engineintake manifold, it may be possible to reduce fuel consumption andprovide system vacuum. In particular, a valve between an engine intakemanifold and a vacuum reservoir may be closed to limit air flow to theengine. Thus, fuel may be conserved because additional fuel may not haveto be delivered to the engine to keep engine exhaust gases substantiallystoichiometric. Further, a vacuum pump can provide vacuum to vehiclesystems while the intake manifold is isolated from the vacuum reservoirvia the valve. In this way, it is possible to reduce engine fuelconsumption and provide vacuum to a vehicle system vacuum reservoir.

The present description may provide several advantages. For example, theapproach may improve engine fuel economy. Further, the approach canprovide additional system flexibility. Further still, the approach mayprovide improved vacuum control during some conditions.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic depiction of an engine;

FIG. 2 shows simulated signals of interest during engine operation;

FIG. 3 shows a high level flowchart of a method for adjusting operationof a vacuum control valve; and

FIG. 4 shows a flowchart of a method for adjusting a vacuum controlvalve in response to vacuum reservoir conditions and a desired flow ratefrom the vacuum reservoir to the engine intake manifold.

DETAILED DESCRIPTION

The present description is related to controlling vacuum used to assistsin actuator operation. FIG. 1 shows one example embodiment forcontrolling vacuum used to assist actuator operation. FIG. 2 showssimulated signals of interest when controlling vacuum within a reservoirthat supplies power to assist in actuator operation according to themethods of FIGS. 3 and 4.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 and exhaust valve 54. Each intake and exhaustvalve may be operated by an intake cam 51 and an exhaust cam 53.Alternatively, one or more of the intake and exhaust valves may beoperated by an electromechanically controlled valve coil and armatureassembly. The position of intake cam 51 may be determined by intake camsensor 55. The position of exhaust cam 53 may be determined by exhaustcam sensor 57.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. Fuel injector 66delivers liquid fuel in proportion to the pulse width of signal FPW fromcontroller 12. Fuel is delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, fuel pump, and fuel rail (not shown).Fuel injector 66 is supplied operating current from driver 68 whichresponds to controller 12. In addition, intake manifold 44 is showncommunicating with optional electronic throttle 62 which adjusts aposition of throttle plate 64 to control air flow from intake boostchamber 46.

Compressor 162 draws air from air intake 42 to supply boost chamber 46.Exhaust gases spin turbine 164 which is coupled to compressor 162.Vacuum operated waste gate actuator 72 allows exhaust gases to bypassturbine 164 so that boost pressure can be controlled under varyingoperating conditions. Vacuum is supplied to waste gate actuator 72 viavacuum reservoir 138, conduit 137, vacuum control valve 144, check valve149, and intake manifold 44. Intake manifold 44 also provides vacuum tobrake booster 140 via conduit 142. Check valve 149 limits air flows frombrake booster 140 to intake manifold 44 and not substantially limit airflow from intake manifold 44 to brake booster 140. Brake booster 140includes a vacuum reservoir and it amplifies force provided by foot 152via brake pedal 150 to master cylinder 148 for applying vehicle brakes(not shown). Vacuum control valve 144 is opened and closed via anelectric signal from controller 12. Brake booster 140 may be suppliedvacuum via pump 141 or intake manifold 44 via restrictor 139, vacuumcontrol valve 144, and check valve 149.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing accelerator positionadjusted by foot 132; a position sensor 154 coupled to brake pedal 150for sensing brake pedal position, a pressure sensor 146 for sensingbrake booster vacuum; a pressure sensor 147 for sensing master cylinderpressure (e.g., hydraulic brake pressure); a knock sensor fordetermining ignition of end gases (not shown); a measurement of enginemanifold pressure (MAP) from pressure sensor 122 coupled to intakemanifold 44; an engine position sensor from a Hall effect sensor 118sensing crankshaft 40 position; a measurement of air mass entering theengine from sensor 120 (e.g., a hot wire air flow meter); and ameasurement of throttle position from sensor 58. Barometric pressure mayalso be sensed (sensor not shown) for processing by controller 12. In apreferred aspect of the present description, engine position sensor 118produces a predetermined number of equally spaced pulses everyrevolution of the crankshaft from which engine speed (RPM) can bedetermined.

In some embodiments, the engine may be coupled to an electricmotor/battery system in a hybrid vehicle. The hybrid vehicle may have aparallel configuration, series configuration, or variation orcombinations thereof. Further, in some embodiments, other engineconfigurations may be employed, for example a diesel engine.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is described merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

Referring now to FIG. 2, simulated signals of interest during engineoperation are shown. Vertical markers T₀-T₇ identify particular times ofinterest during the operating sequence.

The first plot from the top of FIG. 2 shows engine throttle positionversus time. Time starts at the left side of the plot and increases tothe right. Engine throttle position is at its lowest value at the bottomof the plot and increases in magnitude toward the top of the plot. Alower throttle position provides a smaller throttle opening amount. Ahigher throttle position provides a larger throttle opening amount.

The second plot from the top of FIG. 2 shows engine speed versus time.Time starts at the left side of the plot and increases to the right.Engine speed is at its lowest value at the bottom of the plot andincreases toward the top of the plot.

The third plot from the top of FIG. 2 shows engine intake manifoldpressure versus time. Time starts at the left side of the plot andincreases to the right. Engine intake manifold pressure increases in thedirection of the Y-axis arrow. Horizontal marker 202 representsatmospheric pressure in the second plot. Thus, when manifold pressure isabove marker 202 the intake manifold is at a positive pressure. Whenmanifold pressure is below marker 202 the intake manifold is at avacuum.

The fourth plot from the top of FIG. 2 shows vacuum reservoir pressureversus time. Time starts at the left side of the plot and increases tothe right. Horizontal marker 204 represents atmospheric pressure in thefourth plot. Horizontal marker 206 represents a second threshold levelof vacuum reservoir pressure. Horizontal marker 208 represents a firstthreshold level of vacuum reservoir pressure. Vacuum reservoir vacuum isat a higher level of vacuum at the bottom of the plot.

The fifth plot from the top of FIG. 2 shows a vacuum control valvecommand (e.g. valve 144 of FIG. 1). Time starts at the left side of theplot and increases to the right. The vacuum control valve is open whenthe signal is near the top of the plot, and the vacuum control valve isclosed when the signal is near the bottom of the plot.

It should be noted that intake manifold pressure and vacuum reservoirpressure are not plotted to the same scale. For example, the units ofthe Y axis of the intake manifold pressure plot are not equivalent tothe units of the Y axis of the vacuum reservoir plot.

At time T₀, the engine is operating at a medium engine throttle position(e.g., 35% of wide-open-throttle (WOT)). Further, the engine speed is ata medium engine speed (e.g., 2500 RPM), the intake manifold pressure isabove atmospheric pressure, pressure in the vacuum reservoir is betweena first threshold pressure 208 and a second threshold pressure 206, andthe vacuum control valve is in a closed state. In addition, a vacuumpump draws air from the vacuum reservoir while pressure in the vacuumreservoir is above a first pressure threshold 208.

At time T₁, the throttle position is reduced thereby decreasing theintake throttle opening area. Further, engine speed starts to decreaseand engine intake manifold pressure also decreases. Pressure in thevacuum reservoir (e.g., brake booster reservoir or waste gate reservoir;see FIGS. 1 140 and 138) also increases at T₁. The pressure increaseindicates that air is flowing into the vacuum reservoir. In thisexample, the vacuum reservoir pressure increase is related to applyingvehicle brakes. The vacuum control valve is opened near T₁ as the intakemanifold pressure falls below atmospheric pressure. Opening the vacuumcontrol valve allows air to flow from the vacuum reservoir to the engineintake manifold when engine intake manifold pressure is less than vacuumreservoir pressure. As a result, the vacuum reservoir pressure begins tobe reduced shortly after time T₁. Vacuum reservoir pressure continues todecrease in response to the engine intake manifold drawing air from thevacuum reservoir.

At time T₂, the vacuum control valve is closed. The vacuum control valveis closed in response to the throttle opening being less than athreshold amount and the measured or estimated engine air amount beinggreater than the desired engine air amount. The engine air amount isfurther reduced when the vacuum control valve is closed, thereby movingthe measured or estimated engine air amount toward the desired engineair amount. Reducing the measured engine air amount allows less fuel tobe injected to the engine to support stoichiometric combustion. Thus,less fuel may be consumed when the engine air amount is reduced. Itshould also be mentioned that the engine intake throttle issubstantially closed for a substantial amount of time between T₁ and T₃.In some examples an engine intake throttle is substantially closed whena plate of the throttle is positioned against a closing stopper. Inother examples, an engine intake throttle is substantially closed whenthe throttle opening area is less than a predetermined amount, less than3% of WOT for example.

Between time T₂ and T₃ the vacuum reservoir pressure continues todecrease, but at a lower rate. The vacuum reservoir pressure continuesto decrease in response to air being drawn from the vacuum reservoir viaa vacuum pump. The vacuum pump may be mechanically or electricallydriven.

At time T₃, the throttle begins to open while engine speed and engineintake manifold pressure increase. The throttle is adjusted and engineload is at a level that does not require a positive intake manifoldpressure to meet the desired level of engine torque. Therefore, theintake manifold pressure increases but remains below atmosphericpressure. Further, the intake manifold pressure is below the vacuumreservoir pressure so the vacuum control valve is opened to allow airflow from the vacuum reservoir to the engine intake manifold. Furtherstill, the vacuum control valve is opened because the throttle openingis greater than a threshold amount and because the desired engine airamount can be provided while the vacuum control valve is open. Thus, thedesired engine air amount is greater than the air flow from the vacuumcontrol valve to the engine intake manifold. Opening the vacuum controlvalve allows air to pass from the vacuum reservoir to the engine intakemanifold, thereby reducing the vacuum reservoir pressure.

At time T₄, the vacuum control valve is closed since the intake manifoldpressure is higher than the vacuum reservoir pressure. The intakemanifold pressure increases in response to an increase in engine torquerequest. In addition, the pressure in the vacuum reservoir is reduced toless than the first threshold pressure 208. As a result, the vacuum pumpis turned off at T₄ in response to vacuum reservoir pressure being lessthan the first threshold pressure 208.

At time T₅, the desired torque begins to fall as indicated by thereduction in throttle position. Further, the intake manifold pressurebegins to fall but remains above atmospheric pressure and vacuumreservoir pressure. The vacuum reservoir pressure also increases at T₅in response to application of a vehicle brake. The increase in vacuumreservoir pressure causes a controller to restart the vacuum pump.

Between time T₅ and time T₆, engine speed and throttle position brieflydecrease and then increase as time approaches T₆. The vacuum controlvalve remains in a closed position between T₅ and T₆ since intakemanifold pressure is greater than vacuum reservoir pressure. In somesystem configurations where a check valve is placed in line with thevacuum control valve, the vacuum control valve may remain open since thecheck valve can limit air flow from the vacuum reservoir to the engineintake manifold.

At time T₆, the throttle opening area is reduced in response to areduction in the desired engine torque. The engine speed is at a higherlevel at time T₆ when the throttle opening area is reduced.Consequently, the engine intake manifold pressure is reduced to a lowerlevel shortly after time T₆. The vacuum control valve is opened brieflyas intake manifold pressure falls below vacuum reservoir pressure;however, the vacuum control valve closes shortly after opening inresponse to the lower intake manifold pressure. The vacuum control valveis closed so that pressure in the vacuum reservoir does not go lowerthan is desired. In one example, the desired vacuum reservoir pressuremay always be above a predetermined level. In particular, thepredetermined level may be a pressure level that is related to operationof the brake booster or another actuator. The vacuum reservoir pressuredecreases in response to opening the vacuum control valve and vacuumreservoir pressure continues to decrease after the vacuum control valveis closed since the vacuum pump draws air from the vacuum reservoir.

Between T₆ and T₇, the desired engine air amount is less than the amountof air that would be provided if the vacuum control valve were commandedto an open position until just before time T₇ when throttle opening areais increased in response to an increase in desired engine torque.Therefore, the vacuum control valve remains closed until time T₇. Whilethe vacuum control valve is closed, the vacuum pump continues to operateand vacuum reservoir pressure is decreased.

At time T₇, the engine air amount is increased and the intake manifoldpressure is less than the vacuum reservoir pressure so the vacuumcontrol valve is opened. Opening the vacuum control valve can cause airflow from the vacuum reservoir to the engine intake manifold. The vacuumcontrol valve remains open for the remainder of time shown in the plots.

Referring now to FIG. 3, a high level flowchart for adjusting operationof a vacuum control valve is shown. The method of FIG. 3 is executableby instructions of controller 12 of FIG. 1.

At 302, method 300 determines engine operating conditions. Engineoperating conditions include but are not limited to engine speed, engineload, vacuum reservoir pressure, engine intake manifold pressure, intakethrottle position, brake actuator position, and desired engine torque.Method 300 proceeds to 304 after engine operating conditions aredetermined.

At 304, method 300 adjusts vacuum reservoir pressure thresholds foraltitude or barometric pressure. When a vehicle operates at altitudewhere barometric pressure is lower than at sea level, less air isavailable to operate a naturally aspirated engine. Therefore, thethrottle opening area has to be increased at higher altitudes ascompared to at sea level to provide a desired engine air amount at idleconditions. Consequently, the pressure difference between atmosphericpressure and intake manifold pressure is reduced at idle. As such, areduced amount of vacuum may be provided by the engine to evacuate airfrom the vacuum reservoir. Similarly, a vacuum pump may provide areduced amount of vacuum as altitude increases.

Method 300 adjusts vacuum reservoir pressure thresholds in response tobarometric pressure or altitude. In one example, a first pressurethreshold (e.g., see FIG. 2) is increased so that the first pressurethreshold is closer to barometric pressure when a vehicle is operated ataltitude as compared to when the vehicle is operated at sea level.Similarly, a second pressure threshold is also increased in response toa vehicle operating at a higher altitude than sea level. In one example,the first and second pressure thresholds are adjusted based on a valuestored in a table or function. The table or function is indexed bybarometric pressure and an adjustment to the pressure threshold isoutput. Method 300 proceeds to 306 after vacuum reservoir pressurethresholds are adjusted.

At 306, routine 300 judges whether or not engine temperature is lessthan a threshold engine temperature. In one example, the thresholdtemperature is used to determine if the engine is at cold startconditions. If engine temperature is less than the thresholdtemperature, method 300 proceeds to 312. Otherwise, method 300 proceedsto 308.

At 308, method 300 judges whether or not throttle position has beenadjusted since engine start after an engine stop. Method 300 proceeds to310 if throttle position has been adjusted since engine start.Otherwise, method 300 proceeds to 314.

At 310, method 300 adjusts opening and closing of a vacuum controlvalve. In one example, method 300 adjusts the opening and closing of avacuum control valve as is shown in FIG. 2 and in accordance with themethod of FIG. 4. Method 300 proceeds to exit after adjusting the vacuumcontrol valve.

At 314, method 300 closes the vacuum control valve. The vacuum controlvalve is closed at 314 when the engine is started at warm operatingconditions and before the driver or a controller causes the enginethrottle position to be adjusted. Vacuum may be provided to the vacuumreservoir by a vacuum pump when the vacuum control valve is closed. Thevacuum control valve is closed during a warm start before a firstthrottle adjustment since the engine was stopped and the enginerestarted so that the throttle has the capability of adjusting engineair amount to a low level without retarding spark. Once the throttle hasbeen adjusted, the method of FIG. 4 may be used to control the vacuumcontrol valve at 310.

At 312, method 300 opens the vacuum control valve. During a cold enginestart, the engine air amount may be increased during idle conditions tobring the engine up to operating temperature at an increased rate.Therefore, if the engine intake manifold pressure is less than thevacuum reservoir pressure, air can be drawn to the engine intakemanifold via the vacuum control valve. Thus, under some conditions, theintake manifold may increase the vacuum in the vacuum reservoir during acold start. The engine torque may be controlled by retarding spark whichmay further increase the amount of energy transferred from the engine tothe exhaust gas after treatment system.

Referring now to FIG. 4, a flowchart of a method for adjusting a vacuumcontrol valve in response to vacuum reservoir conditions and a desiredflow rate from the vacuum reservoir to the engine intake manifold isshown. The method of FIG. 4 is executable by instructions of thecontroller of FIG. 1.

At 402, method 400 determines engine operating conditions. Engineoperating conditions include but are not limited to engine speed, engineload, vacuum reservoir pressure, engine intake manifold pressure, intakethrottle position, brake actuator position, and desired engine torque.Method 400 proceeds to 404 after engine operating conditions aredetermined.

At 404, method 400 judges whether or not manifold absolute pressure(MAP) is greater than vacuum reservoir absolute pressure. If method 400judges MAP is greater than vacuum reservoir absolute pressure, method400 proceeds to 416. Otherwise, method 400 proceeds to 406.

At 406, method 400 judges whether or not additional vacuum from theintake manifold is desired. In a first example, additional vacuum in thevacuum reservoir is not desired to be supplied by the engine intakemanifold when the engine speed is higher and the intake throttle openingamount is small. For example, additional vacuum supplied by the engineintake manifold is not desired when engine speed is greater than 3500RPM and the engine throttle opening amount is less than 5% of WOT. Inanother example, additional vacuum in the vacuum reservoir is notdesired to be supplied by the engine intake manifold when the enginespeed is low, the throttle opening amount is low, and when the engineair amount is greater than the desired engine air amount. For example,additional vacuum supplied by the engine intake manifold is not desiredwhen engine the engine is at idle (e.g., less than 900 RPM) and thethrottle opening amount is less than 3% of WOT. In other examples, itmay be judged that air flow from the vacuum reservoir to the engineintake manifold is not desired when the desired engine air amount isless than a predetermined threshold engine air amount. If method 400judges additional vacuum from the intake manifold is desired during thepresent engine operating conditions, method 400 proceeds to 412.Otherwise, method 400 proceeds to 408.

At 408, method 400 closes the vacuum control valve. In examples wherethe vacuum control valve is normally open, the vacuum control valve canbe closed by applying an electrical signal to the vacuum control valve.In examples where the vacuum control valve is normally closed, thevacuum control valve can be closed by removing an electrical signal fromthe vacuum control valve. Method 400 proceeds to 410 after closing thevacuum control valve.

At 410, method 400 compensates for closing the vacuum control valve bycompensating for any air flow change into the intake manifold from thevacuum reservoir by increasing the engine throttle opening amount. Inone example, the air flow from the vacuum reservoir to the engine intakemanifold can be determined by indexing a function that describes flowfrom the vacuum reservoir to the engine intake manifold based on thepressure difference between the vacuum reservoir and the engine intakemanifold. The intake throttle position can be adjusted via a functionthat outputs throttle position based on a desired throttle flow rate andthe pressure differential across the throttle. Thus, the air flow ratefrom the vacuum reservoir to the engine intake manifold can be added tothe desired throttle flow rate to determine the adjusted throttleposition.

At 412, method 400 opens the vacuum control valve. In examples where thevacuum control valve is normally open, the vacuum control valve can beopened by removing an electrical signal to the vacuum control valve. Inexamples where the vacuum control valve is normally closed, the vacuumcontrol valve can be opened by applying an electrical signal to thevacuum control valve. Method 400 proceeds to 414 after opening thevacuum control valve.

At 414, method 400 compensates for opening the vacuum control valve byreducing air flow to the intake manifold from other sources (e.g.,throttle, PCV valve, bypass air valve). The air adjustment to the intakethrottle position or other air flow control device is effected asdescribed at 410. In addition, the vacuum pump may be activated at 414if desired.

At 416, method 400 closes the vacuum control valve. The vacuum controlvalve is closed as described at 408. At 418, air flowing into the engineintake manifold is adjusted by changing the position of an intakethrottle or other device as described at 410. Method 400 proceeds to 420after the vacuum control valve is closed and the engine intake air flowis adjusted.

At 420, method 400 judges whether or not pressure in the vacuumreservoir is less than a first threshold level. If so, method 400proceeds to 422. Otherwise, method 400 proceeds to 424.

At 422, method 400 deactivates a vacuum pump in systems where a vacuumpump is present. If the vacuum pump is electrically driven, electricalpower is removed from the vacuum pump. If the vacuum pump ismechanically driven, a clutch or cam profile may be adjusted todeactivate the vacuum pump. Method 400 proceeds to exit after the vacuumpump is deactivated.

At 424, method 400 judges whether or not vacuum reservoir pressure isless than a second threshold amount (e.g., see FIG. 2 at 206). If method400 judges vacuum reservoir to be less than the second threshold amount,method 400 proceeds to 426. Otherwise, method 400 proceeds to 432.

At 426, method 400 maintains the vacuum pump in the same operatingstate. For example, if the vacuum pump is activated at 428, the vacuumpump remains activated and method 400 proceeds to exit. On the otherhand, if the vacuum pump is deactivated at 422, the vacuum pump remainsdeactivated and method 400 proceeds to exit.

At 428, method 400 activates the vacuum pump. In examples where thevacuum pump is electrically driven, a voltage is applied to the vacuumpump. In examples where the vacuum pump is mechanically driven, a clutchor cam device couples the vacuum pump to the mechanical power source.Method 400 proceeds to exit after the vacuum pump is activated.

Thus, when MAP is not greater than vacuum reservoir pressure, the stateof the vacuum control valve is determined in response to whether or notadditional vacuum from the engine intake manifold is desired under thepresent engine operating conditions. Further, is should be noted thatoperations 416-428 may replace 408 and 410 in some examples so that thevacuum pump can be deactivated, activated, or maintained in a presentstate, depending on first and second vacuum reservoir pressurethresholds when MAP is not greater than vacuum reservoir pressure. WhenMAP is greater than vacuum reservoir pressure, the vacuum control valveis closed and the state of the vacuum pump is varied in response tovacuum reservoir pressure.

As will be appreciated by one of ordinary skill in the art, the methodsdescribed in FIGS. 3-4 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,single cylinder, I2, I3, I4, I5, V6, V8, V10, V12 and V16 enginesoperating in natural gas, gasoline, diesel, or alternative fuelconfigurations could use the present description to advantage.

1. An engine operating method, comprising: operating an engine at acondition where an intake throttle is substantially closed; closing avalve to limit engine air flow from a vacuum reservoir to an engineintake manifold when a pressure in the engine intake manifold is lessthan a pressure in the vacuum reservoir; and decreasing the pressure inthe vacuum reservoir via a pump when the valve is closed.
 2. The engineoperating method of claim 1, where a desired engine air amount is lessthan an amount of air flowing into an engine intake manifold via theclosed intake throttle and the valve.
 3. The engine operating method ofclaim 1, where the vacuum reservoir is a turbocharger waste gate vacuumreservoir or a brake booster.
 4. The engine operating method of claim 1,further comprising at least partially opening the valve in response toan increase in engine load.
 5. (canceled)
 6. The engine operating methodof claim 1, further comprising increasing an intake throttle openingamount in response to closing the valve.
 7. The engine operating methodof claim 2, where a position of the substantially closed intake throttlevaries with barometric pressure.
 8. An engine operating method,comprising: boosting engine intake air; during a first condition:operating an engine at a condition where a desired engine air amount isless than an amount of air flowing into an engine intake manifold via asubstantially closed intake throttle and a valve; and closing the valveto limit engine air flow from a vacuum reservoir to the engine intakemanifold when a pressure in the engine intake manifold is less than apressure in the vacuum reservoir; and during a second condition:operating the engine at a condition where the desired engine air amountis less than the amount of air flowing into the engine intake manifoldvia the substantially closed intake throttle and the valve; and openingthe valve to increase engine air flow from the vacuum reservoir to theengine intake manifold when the pressure in the engine intake manifoldis less than the pressure in the vacuum reservoir.
 9. The engineoperating method of claim 8, further comprising operating the engineless efficiently during the second condition.
 10. The engine operatingmethod of claim 9, where the engine is operated less efficiently byincreasing an amount of engine spark retard.
 11. The engine operatingmethod of claim 8, where the second condition is after an engine startand before a first depression of an accelerator pedal.
 12. The engineoperating method of claim 8, where the first condition is after a firstdepression of an accelerator pedal.
 13. The engine operating method ofclaim 12, where the vacuum reservoir is a brake booster or aturbocharger waste gate vacuum reservoir.
 14. An engine vacuum system,comprising: an engine with an intake manifold; a turbocharger having aturbine coupled upstream of the intake manifold; a vacuum pump; a vacuumreservoir, the vacuum reservoir in communication with the intakemanifold via a first conduit, and the vacuum reservoir in communicationwith the vacuum pump via a second conduit; a first valve located alongthe first conduit; and a controller, the controller includinginstructions for opening the first valve when a pressure in the intakemanifold is less than a pressure in the vacuum reservoir, the controllerincluding instructions to close the first valve when pressure in theintake manifold is less than pressure in the vacuum reservoir and whenadditional vacuum in the vacuum reservoir is not desired.
 15. The enginevacuum system of claim 14, where the controller includes furtherinstructions for determining additional vacuum in the vacuum reservoiris not desired when an intake throttle opening is less than a thresholdamount and engine speed is higher than a threshold amount.
 16. Theengine vacuum system of claim 14, further comprising a check valvelocated along the first conduit.
 17. The engine vacuum system of claim14, where the controller includes further instructions for operating theengine at a low load condition where an opening amount of an intakethrottle is less than a threshold amount, and closing the first valve tolimit engine air flow between the vacuum reservoir and the intakemanifold when the pressure in the intake manifold is less than thepressure in the vacuum reservoir.
 18. The engine vacuum system of claim14, where the vacuum reservoir is a brake booster or a turbochargerwaste gate vacuum reservoir.
 19. The engine vacuum system of claim 14,further comprising a pressure sensor located to sense the pressure ofthe vacuum reservoir.
 20. The engine vacuum system of claim 14, wherethe controller includes further instructions for closing the first valvewhen brake booster pressure rises in response to depressing a brakepedal.